Hi,
That´s a difficult question

Well, the truth is, there no best extension. As you have already noticed, every extension has its strength(s) depending on kind of your photos and also on your requirements and taste. I´ve already utilized these extensions for a large amount of photos and still do not have any distinct favourite
In general If you like to achieve overall "punchy", vivid pictures out of the box, then maybe PerfectlyClear would be your choice.
Xe847ProPlus however is great for photos with a great share of blue color (e.g. blue sky, sea etc...) and color cast. It simulates the way how human´s brain is seeing and thus works well in removing color casts. Besides it does not sharpen the photos, which is good, if you would like to postprocess your pictures more later. Of course you can also turn off the sharpening in the 2 other extensions, too.
i2E is suited for enhancing and optimizing photos, which should be printed out. Accordingly i2E´s sharpening is more stronger than PerfectlyClear´s and of course Xe847ProPlus´s in the default setttings. Besides, green is the color i2E likes the most. So if you have photos that have a lot of green areas (e.g. grass, trees etc.), i2E might be your choice.
These 3 extensions also complement each other very well in batch processing.
According to my experience PerfectlyClear would achieve the overall most obvious enhancement of your photos and automatically remove red eyes effects but at the expense of speed.
XE847ProPlus is the fastest with more gentle enhancements whereas i2E(Pro) is a good mixture between speed and enhancement degree.
Hope this helps clarifying a bit. But why don´t you just trial out these 3 extensions and find out what suits you best? They are already bundled within PhotoPerfect. The only restrictions in the trial version is watermarks in photos processed with i2e and PerfectlyClear. Xe847 is free. You have to upgrade to the ProPlus version, if you would like to adjust the parameters manually.